Describe 2 theories of the function of sleep and evaluate them in relation to evidence from sleep deprivation studies

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Describe two or more theories of the function of sleep and evaluate them in relation to the .

evidence coming from sleep deprivation studies.

One theory of the function of sleep is the energy conservation theory (Webb). Warm – blooded animals, such as humans use up a lot of energy to maintain a constant body temperature. This is especially difficult for small animals with a high metabolic rate. All activities use energy, and animals with a high metabolic rate use even more energy when scavenging and hiding or escaping from predators. Sleep, however, provides a period of enforced inactivity (therefore using less energy), much like hibernation. This means that it is a way of conserving energy and may provide explanation towards the function of sleep.

We can see that this has a certain amount of face validity if we compare sleep patterns in different species. It has been noted that the percentage of sleep varies according to the size of a species. The amount of sleep is further affected by two other external factors: food requirements and predator avoidance.

For example, cows and horses (grazing animals) have to spend a lot of their time eating because the food that they eat, such as grass and plants, is low in nutrients and so they need to eat a lot of the time and therefore have less time to sleep. However, carnivores such as cats and dogs eat a more balanced and healthy diet and so do not need to spend all of their time eating. This means that they can have afford to have more sleep and can therefore conserve more energy.

Sleep is also affected by the status of predator or prey. If an animal is a predator, then it can spend more time sleeping because they don’t need to worry about being hunted. Animals that are preyed on spend more time being vigilant to avoid predators. In an ideal situation, these animals would not sleep at all because it is dangerous, but realistically, they must sleep when they are in the least amount of threat. Meddis (1975) even suggested that sleep helps prey animals to avoid the predators when they are most vulnerable. This can suggest why some animals are nocturnal and choose to sleep during the day and hunt at nighttime and may be used to explain the function of sleep.

However, when considering energy conservation, we should acknowledge that there is a distinct difference between REM and NREM sleep. The brain uses up a lot of energy and the amount of energy it uses up only drops significantly in NREM sleep, as REM brain waves remain very similar to those of a fully active and functional brain. This means that the theory cannot be used to fully explain the function of sleep and may only explain why we have NREM sleep.  

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This view was supported by Allison and Cicchettie (1976) who found that larger animals had less NREM sleep, because they don’t need to conserve as much energy as those with a high metabolic rate. This shows that it is NREM sleep that is important for energy conservation and can therefore partially contribute to the explanation of the function of sleep.

On the other hand, it has been found that sleep does not conserve a great deal more energy than when resting, sleep reduces energy rates by 5-10%. This suggests that rest would be just as adaptive as sleeping. Further criticism ...

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